The present invention relates to the field of chemical mechanical polishing/planarization (CMP). More particularly, the present invention relates to a CMP tool, used in semiconductor manufacturing, having the ability to improve the planarization ability of a CMP machine while maintaining uniformity of material removal across the wafer.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual integrated circuit chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithographic process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. The need for a precise image projection is accentuated with the current drive toward smaller, more complex integrated circuit (IC) designs.
In modern IC fabrication technology, it is presently necessary to form various embedded structures over previous material layers of integrated circuits formed on semiconductor wafers. Integrated circuits on semiconductor wafers are also commonly constructed in layers. Each layer of the circuit can create or add unevenness to the wafer as it is constructed. Slight irregularities on the wafer surfacexe2x80x94or on deposited filmsxe2x80x94can distort semiconductor patterns as lithographic equipment and processes transfer these patterns to the wafer surface. For this reason, during the manufacturing process, certain portions of these material layers typically require complete or partial removal to achieve the desired device structure on the wafer. Any imperfections are preferably smoothed out before generating the next circuit layer.
Chemical mechanical polishing/planarization (CMP) has become a popular method to achieve this material removal and to prevent distortion. CMP techniques are used to planarize the raw wafer and each layer of material added thereafter to a flat, uniform finish. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad that is moving in the plane of the wafer surface to be planarized. Typically, a polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish and planarize the surface of the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer.
The polishing pads commonly used in this process include both belt-type pads and rotary-type pads. A belt-type pad typically consists of one or more sections of material that are joined together through lamination or the like to form a belt. The belt is placed around a plurality of rollers that cause the belt to rotate. A rotary-type pad typically consists of one or more sections of material that are joined together to form a pad. The pad is attached to a rotary machine that rotates the pad to polish a wafer.
Typical wafer polishing machines and processes are highly sensitive to the density of structures underlying the layer being polished. For example, the wafer polishing machines and processes typically exhibit high material removal rates in sparse areas and relatively low material removal rates in dense areas. The resulting variation in film thickness across the dies degrades device performance and limits the ability to continue stacking additional layers on the wafers during fabrication processes. Accordingly, polishing machines and processes that overcome these deficiencies are needed.
It would be desirable to improve the planarization performance of CMP polishers while maintaining a desirable level of uniformity of material removal across the entire wafer.